Erasable paper and process for making same

ABSTRACT

Process for making erasable paper by forming a paper web, contacting the formed web with a parchmentized solution, removing excess acid, at least partially drying the web, and applying to a surface of the paper one or more sizing agents which are low molecular weight polyesters made by reaction of rosin and maleic anhydride adducts with polyhydric alcohols, and are preferably polyesters of rosin-maleic anhydride adducts with aliphatic polyols, and are applied alone or in combination with certain additives. The invention also includes the product of the foregoing process.

United States Patent Inventors William R. Wasko Cherry Hill; Milton R.Sheppard, Willingboro, N..I.; Orsi R. Schultz, Philadelphia, Pa.; Sol A.Albertson, Willingboro, NJ.

Appl. No, 698,474

Filed Jan. 17, 1968 Patented Sept. 21, 1971 Assignee Paterson ParchmentPaper Company Bristol, Bucks County, Pa.

ERASABLE PAPER AND PROCESS FOR MAKING SAME 8 Claims, 1 Drawing Fig.

U.S.Cl 162/135, 8/119,117/153,162/158,162/162,162/164,162/168,162/180,162/181R,162/184 Int. Cl D21h 3/34, D21f1l/00 Field ofSearch 162/ 1 64,

179,184,187,182,136,158,l62,178, 180,135; 8/ll9;117/153 STOCKPREPARATION [56] References Cited UNITED STATES PATENTS 2,156,755 5/1939Fuelncgg...................... 117/153 2,721,505 10/1955 Yngve 162/1643,184,373 5/1965 Arledter 162/178 X 3,459,743 8/1969 Zussman 162/162 XOTHER REFERENCES Casey, Pulp & Paper," Vol. II, 2nd ed., 1960lnterscicnce Publishers, Inc. NY. page 654 Primary Examiner$. LeonBashore Assistant ExaminerFrederick Frei Atwrm'yJames Albert DrohilePAPER FORMATION ACID (CONCENTRATEDI CONTACTING OPTIONAL STOCKMODIFICATION PAPER WEB ACID (DI LUTEI CONTACTING ALTERNATE AC I DREMOVAL WASHING PRE- DRYING jsuRFAcE SIZING DRYING PRoouerPAPIsRPATENTED SEPZI l9?! 3 507,521

S TQCK PREPARATlON l PAPER WEB AC I D (CONCENTRATED) CONTACTINGALTERNATE (DILUTE) CONTACTING ACID REMOVAL WASHING PRE- DRYING SURFACE5| Z ING 1 INVENTORS WILLIAM R. WASKO MILTON R. SHEPPARD ORSI R. SCHULTZsoL A. ALBERTSON DRYING BY WM ATTORNEY.

1 PRODUCT PAPER ERASABLE PAPER AND PROCESS FOR MAKING SAME SUMMARY OFTHE INVENTION BACKGROUND OF THE T ON it has been found that, bysubjecting paper to contact for a defined period of time with arelatively concentrated aqueous Flak! of sulfuric acid solution ofdefined strength, the paper is The instant invention relates tocellulosic sheet materials rendered more readily eras-ah, panicmaflywith respect m such as paper. More particularly, it is directed to aovel writypewrmhg' h also has been found that paper base stocks or ingpaper having superior erasability characteristics, and to furnishes,Whihh have been mod-fled in a novel way h thc P f mak'ng Paper additionof certain additives provide superior and therefore Descmmon ofpreferred base stocks for making more readily erasable paper Hcrewfore'f f f' been made pmduFe a wmmg in accordance with the present invention.Specifically, it has Paper from much typewmmg could be erased easflyafld prac' been found that practice of the latter, preferred embodimentCally completely by means a rubber Tamer than of the instant inventionresults in the production of product an f of the hard such as commonlypapers which exhibit superior whiteness and opacity,as well as requlredthe erasure 9 typewmlmg' These superior erasability, rendering themparticularly suitable for have involved the application of a thincoating of suitable size, commercial Sale and use as a writing Paper andpaniculafly as Such as gum Surface f of a typewriter paper. Furthermore,it also has been found that the paper sheet. lt hasbeen suggested thatthis prior coating thmugh the application of a Sma" amount of one ormore technique depend? for effectwmess "P the Presence ofa selectedsizing agents to the surfaces of the paper after acid Supenmposediumform' 9 of Sue on Surfaces of contact and removal, and after at leastpartial drying the tenthe P P f' whereby P P from ready access dencicsof typing inks to smudge and "feather" or wick" on by consmuems of mk Wotherw'se would Panetmtc the product paper, and to be received unevenlyacross the surthe paper and render the wmmg mdehblg' face thereof, aremarkedly reduced over those observed with in accordance wnh pastpracnce' asomewha readly such paper which is not so coated. Accordingly.the latter ble writing paper has been produced by dipping the paper in atechnique constitutes an essential element of the present insolution ofa suitable size coating, followed by removal of the Random excesscoating. This operation is repeated several times in order to build up asufficiently heavy layer of coating to give DESCRIPTION OF THE DRAwmGthe desired degree of erasability. More recently, the coating techniquehas been modified so as to constitute one eontinuous operation involvinga series of brief dippings. Great care must be taken in practicing thecoating method to ensure application to the paper of the proper amountof size, since too little size coating does not give the desired degreeof erasability and too much will cause the ink to smear excessively. Thethickness of the size coating ultimately built up upon the surfaces ofthe paper is controlled, to some degree, by regulating the viscosity ofthe coating solution within defined limits.

Readily erasable papers heretofore made suffer from a number of distinctand significant disadvantages. First of all, with the prior technique itis very difficult, if not impossible, to ensure a uniform erasabliitycharacteristic from one surface of the paper sheet to the other, andfrom end to end on a roll of paper. This failing arises from theimpossibility of providing an absolutely uniform thickness of size onall surfaces of the paper. A further failing of prior readily erasablepapers is their tacky" feel and their susceptibility to moisture. inaddition, it has been found that the coating sizes commonly employed inprior techniques have a tendency to discolor and become Paper- Theaccompanying drawing illustrates schematically the practice of theinstant invention in its several embodiments, and the positioningthereof in the sequence of conventional papermaking operations. Thus,practice of the preferred technique herein disclosed, of modifying thepaper base stock through the addition thereto of one or more of certainadditives, takes place during the steps constituting the conventionalstock preparation and prior to the conventional paper formation step.Following formation, the web of paper is contacted with the relativelyconcentrated aqueous solution of 40 sulfuric acid, and the acidsubsequently removed by one of several alternate techniques such as bycontacting with a relatively dilute aqueous solution of sulfuric acid,by neutralization of the residual acid, or the like. Following theremoval 01 the residual acid, the paper web is washed and at leastpartially dried preliminary to the surface application, as herein disclosed, of a selected sizing agent by conventional technique: andapparatus. Follow such surface application, the drying i completed, ifnecessary, to produce the finished produc somewhat brittle on aging,causing the coated paper also to DETAILED DESCRIPTIQN OF THE NVENTIONbecome more yellow and brittle with age than normally would be expected.Still another disadvantage is the tendency of in practicing the instantinvention, paper is contacted for present day size coatings to cause thecoated paper to become defined period of time with a contacting agentconsisting e: more transparent, which also is undesirable in mostwriting sentially of aconcentratcd aqueous solution of sulfuric acid(papers. specified strength. Normally, aqueous sulfuric acid solutior Inview of the above, it is a principal object of the present in'containing from about to about 77 percent by weight of su stantinvention to provide a novel and improved writing paper, furic acidprovide satisfactory results and can be used. Ho\ including particularlyan improved paper for typewriting, and ever, sulfuric acidconcentrations in the range of from abo a novel method of preparing andtreating paper to achieve this ,0 to about 72 percent by weight givesuperior results ar result. A further and more specific object is toprovide a novel therefore are preferred for use. Under certaincircumstance writing paper exhibiting superior erasabilitycharacteristics however, aqueous sulfuric acid solutions having concentrwith respect to typewriting, resistance to smudging and tions ofsulfuric acid either above or below the above-recit feathering by typinginks, and more uniform receptivity to ranges also may providesatisfactory results. typewriting. Still another and major object is toprovide a new 65 it is critical to the achievement of satisfactoryresults in t and improved paper, including particularly a typewritingpractice of the instant invention that the paper remain in cc paper, anda novel procas for making same, which tact with a concentrated aqueoussulfuric acid solution preferentially in the practice of the inventioninvolves modifisuitable strength for a sufficient but limited period oftin cation of the base paper stock or furnish, as well as treat- Thus,the total contact time between the paper and I ment of the paper formedtherefrom, in order to achieve suspecified acid solution should besomewhere in the range perior whiteness and opacity in addition tosuperior erasability from about i to about 20 seconds. Contact timessomewha in the product paper. These and other objects and advantagesexcess of I second, for example between 4 and i2 secon of the instantinvention will become more readily apparent provide superior results andare preferred, although the c from the following detailed description ofthe invention, which tact time normally should not exceed 20 seconds.Genera is to be read in the light of the accompanying drawing. 75 thecontact time required to give satisfactory results will v:

within the recited range, inversely as the strength of the concentratedaqueous sulfuric acid solution is varied within its above-specifiedrange. Thus, concentrations of acid in the lower portion of the range.Thus, concentrations of acid in the lower portion of the range indicatedto be suitable will require contact times in the upper portion of thesuitable range of times, and vice versa. For acid concentrations in thepreferred range of from about 65 to about 72 percent by weight ofsulfuric acid, contact times of from about 5 to about seconds have beenfound to provide excellent results.

The temperatures at which the contacting of the paper with therelatively concentrated acid solution takes place is not particularlycritical. Generally, however, an increase in contact temperature hasbeen found to be helpful in producing satisfactory results where it isdesired to compensate for a decrease in suitable acid strength, orsuitable contact time, or both. Contact temperatures in the range offrom about 50 F. to about 70 F. produce satisfactory results and can beemployed, although contact temperatures in the range of from about 55 F.to about 65 F. are preferred. On occasion, contact temperatures outsideof the aforementioned ranges can be employed.

Contacting between the concentrated aqueous solution of sulfuric acidand the paper can be effected by suitable conventional techniques andapparatus. Normally, the contacting will be accomplished by immersing ordipping the paper in a liquid phase or bath consisting essentially ofthe concentrated aqueous solution of sulfuric. acid and leaving thepaper in contact with the acid, either immersed or simply wet with theacid, for the required contact time and under the recommended contacttemperatures. This contacting may be batch-wise, although continuousoperation is preferred, involving continuously passing the paper throughthe acid bath, which is either contained or flowing concurrently orcountercurrently with the web of paper.

After the paper has been sufficiently contacted with the concentratedaqueous solution of sulfuric acid, it can be subjected to conventionaltechniques and apparatus to remove substantially all of the remainingacid solution. Such techniques include, for example: thoroughly washingthe contacted paper with water; neutralizing the residual acid with asuitable alkaline material, followed by washing with water; and thelike. Another, and preferred, alternative is to contact the papercontaining the residual, relatively concentrated aqueous sulfuric acidsolution first with a relatively dilute aqueous solution of sulfuricacid, and finally with water in order to remove substantially allremaining traces of acid. This alternative is carried out convenientlyby a succession of contacts, in overall countercurrent relationship,between the paper containing the residual, relatively concentratedaqueous sulfuric acid solution and a stream of water which becomesprogressively rich in sulfuric acid with each successive contact withthe paper. In any event, the paper ultimately is dried by conventionalmethods and apparatus. After at least partial drying is effected,however, it is necessary to make the beforementioned surface applicationof the selected sizing agent.

Paper which has been treated with relatively concentrated aqueoussulfuric acid solution in accordance with the present invention exhibitserasability characteristics, particularly with respect to typewriting,which are superior to those possessed by paper rendered more readilyerasable by techniques heretofore known in the art. Thus, by theacid-contacting technique of the present invention it is possible, andindeed normal, to produce a product paper exhibiting an erasabilitywhich is absolutely uniform from one surface of the paper to the other,and from end to end on a large roll of paper. This is in decidedcontrast to papers rendered more readily erasable by conventionalcoating techniques, where the thickness and evenness of the coating, andconsequently the unifomiity of the erasability, very often varies fromsurface to surface and from end to end on the paper. In addition, papertreated with sulfuric acid in accordance with the present invention doesnot exhibit the same tendency to discolor and become brittle with age asdo conventionally coated papers, and does not show the samesusceptibility to moisture and tendency to feel tacky" to the touch asthe conventional coated papers. Furthermore, by the instant technique ofapplying a selected sizing agent to the surface of the acid-treatedpaper, the tendency of typewriting to smudge and feather" or wick onsuch paper is markedly reduced.

While the erasability characteristics of any paper can be substantiallyimproved by subjecting it to treatment in ac cordance with the instantinvention, it also has been found that when conventional paper stocksare modified as hereinafter described, a base paper stock or furnish isproduced which exhibits superior qualities with respect to its use informing paper to be further processed in accordance with the presentinvention. This method of paper stock modification followed by acidtreatmcnt and surface sizing constitutes a preferred embodiment of theinstant invention, in that it produces a product paper exhibiting amongother things superior opacity and whiteness for commercial use and saleas typewriter paper.

in general, it has been found that by incorporating small but sufficientamounts of one or more of certain additives into conventional paperstocks comprising for example either wood or rag pulps, a paper can beconventionally formed which, upon acid treatment in accordance with thepresent invention, also exhibits a superior whiteness and opacity inaddition to more ready erasability. Paper stock modification inaccordance with the instant invention is particularly beneficial withrespect to parchmentizcd papers. This is for the reason that paperstocks of the absorbent paper type, such as are commonly employed inmanufacturing parchmentizcd papers, typically produce a paper ofcommercially undesirable translucency after acid treatment to improveerasability.

in accordance with the preferred embodiment of the present invention, animproved paper stock is prepared by incorporating one, some orpreferably all of the following additive materials in a stock comprisingrag or wood pulp: l a small amount, sufficient to reduce significantlypaper trans parency, of an opacifying filler or pigment; (2) a smallamount, sufficient to reduce significantly paper absorbency, ofa sizingagent; (3) a small amount, sufficient to improve significantly paper wetstrength, of a wet strength improving agent; and (4) a small amount,sufficient to improve optical brightness, of an optical brighteningagent.

Opacifying fillers or pigments which are suitable for use in accordancewith the invention are those which do not react with acids and which, insmall but sufficient amounts, impart the desired degree of opacity tothe product paper. Suitable fillers include naturally occurringinorganic substances, such as talc, silica, certain clays and the like,or synthetic substances such as barium sulfate, titanium dioxidepigments and the like. The use of an opacifying agent is optional butpreferred in the practice of the instant invention, and the use oftitanium dioxide as a filler is distinctly preferred. Generally, theopacifying filler, for example titanium dioxide, is incorporated in thepaper stock in a small but sufficient amount, generally equivalent tofrom about 2 to about 8 percent by weight of the pulp on a dry basis.Amounts of the opacifying filler approximating 5 percent by weight ofthe dry pulp give excellent results and are preferred. It also iscontemplated as within the scope of the instant invention to incorporatein the paper stock pigments or fillers other than white in color, inorder to produce product papers having a desired color.

Sizing agents, or sizes as they often are called, which are suitable foruse in modifying the paper stock in accordance with the instantinvention are those which, in small but sufficient amounts, are capableof suitably reducing the permeability of the formed paper to subsequentpenetration by the liquids, and in particular by the concentratedaqueous solution of sulfuric acid. Suitable sizing agents, or sizes, aregenerally well known, and include substances such as rosin sizes, animalglues, starches, gelatin, wax emulsions, fatty acid-amine condensatesand the like. Aqueous emulsion polymers which do not undesirably colorthe stock also are suitable, such as aqueous emulsions of: acrylicpolymers (for example, "Goodrich 2,600 X84); Buna rubber (for example,HYCAR 1,552"); butadiene polymers and copolymers (for example, Dow636"); rubber latex; and the like. ln the practice of the presentinvention, the use of a sizing agent, and particularly of a rosin size,is distinctly preferred.

The exact amount of the sizing agent required to be added to the paperstock or furnish to order to impart a sufficient reduction in paperabsorbency can be determined readily by experiment. Generally, however,amounts of the sizing agent, for example, rosin size, equivalent to fromabout V4 to about 3 percent by weight of the pulp on a dry basis aresuitable, although amounts equivalent to approximately 2 percent byweight of dry pulp give excellent results and are preferred. If desired,the necessary amount of size also can be reduced by an increase in theseverity of the stock preparation conditions, for example, by anincrease in beating, to produce a more dense and, consequently, lessporous paper.

The wet strength agent to be added to the paper stock in practicing theinstant invention can be any such known agent which, in small butsufficient amount, is suitable for imparting the desired improvement inwet strength necessary to sustain the paper during subsequent acidtreatment in accordance with the instant invention. Wet strength agentsare well known in the art. See, for example, U.S. Pat. Nos. 3,129,133;3,146,158; and 3,151,017 for many specific examples of suitable wetstrength agents. Melamine formaldehyde resins are urea formaldehyderesins which are water dispersible and of suitable quality have beenfound to be particularly useful. Generally, the amount of the wetstrength agent required to be incorporated in the paper stock to impartthe desired degree of improvement in paper wet strength can bedetermined readily by experiment. However, the usual wet strength agentsnormally are incorporated in paper stock in amounts equivalent to fromabout V4 to about 3 percent by weight of the paper pulp on a dry basis,and suitable melamine formaldehyde resin and urea formaldehyde resin wetstrength agents are satisfactorily employed in amounts approximating 2percent. The use of a wet strength agent in the practice of theinvention is distinctly preferred.

Optical brightening agents which are suitable for use in modifying thepaper stock in accordance with the instant invention are those which, insmall but sufficient amounts, are capable of improving the opticalbrightness and color uniformity of the product paper to the desireddegree. Suitable optical brightening agents are generally well known andin clude substances such as the sodium salt of triazinyl diaminostilbene disulfonic acid. The use of an optical brightening agent in thepractice of the present invention is optional but preferred, and the useof the sodium salt of triazinyl diamino stilbene disulfonic acid isdistinctly preferred. Such an optical brightening agent is availablecommercially from Sandoz, Ltd., of Basle, Switzerland, under the brandname, LEU- COFOR B." The exact amount of the optical brightening agentrequired to be added to the paper stock in order to impart the desiredimprovement in optical brightness and color uniformity can be determinedreadily by experiment. Generally, however, amounts of the selectedoptical brightening agent, such as for example, the sodium salt oftriazinyl diamino stilbene disulfonic acid, of from 0.5 to about 2.0ounces by weight per 100 pounds of the pulp on a dry basis are suitable,although amounts equivalent to approximately 1 ounce by weight on thesame basis give excellent results and are preferred.

in practicing the instant invention, the above-mentioned additivematerials are incorporated in the stock preparation state, i.e., duringthe conventional beating or refining operations, or in both. In thismanner the additives are uniformly distributed throughout the stock, andultimately throughout the paper after the latter is formed byconventional techniques and machines.

Conventional paper stocks comprising rag or either hard or soft woodpulps can bc used in the practice of the present invention. For example,suitable pulps include bleached and semibleached sulfate and sulfitefiber pulps and blends thereof with each other and the like. Pulp fibersknown and available commercially under such brand names as VlGORWHlTE,"CEDANlER,"c Brunswick," all of which are percent softwood bleachedsulfate pulps, and "ESPANOLA which is a 50/50 blend of bleached hardwoodand bleached softwood, produced by a sulfate process can conveniently beused.

As noted above, the acid contacting in accordance with the presentinvention of a paper made from either a nonmodified or modified paperstock produces a marked improvement in tlfe erasability of such paper,particularly with respect to typewriting, The modification of the paperstock as herein disclosed provides an additional benefit in that theproduct paper exhibits superior opacity, superior whiteness orbrightness, and greater wet strength, all of which makes such paper moreattractive from a commercial standpoint. However, it also has beenobserved that a paper rendered more readily erasable by practice of onlythe acid-containing technique of the present invention exhibits anundesirable susceptibility to smudging by the usual typing ink, and towicking" or feathcring by such inks, particularly after erasure andretyping. Accordingly, while the erasability characteristics of theacid-treated paper were superior and indeed outstanding, the significanttendency of such paper to promote smudging and wicking or feathering oftyping inks lcft something to be desired.

As heretofore noted, it also has been found that the tendency of theacid-treated paper to promote ink smudging and wicking or feathering canbe substantially eliminated or significantly reduced by the technique ofapplying one or more selected sizing agents to the surface of theacid-contacted paper following acid removal and washing, and after atleast partial drying of the paper.

Although a number of "zing agents have been tested, the sizing agents todate found most suitable are: the relatively low molecular weightpolyesters made by reaction of rosin and malcic anhydride adducts withpolyhydric alcohols or polyols and including, for example, suchpolyesters with aliphatic diols, triols and other polyols such asethylene glycol, glycerine, sorbitol, mannitol, pcntaerythritol and thelike, with aromatic polyols such as phenol, catechol, rcsorcinol andhydroquinol, and with mixtures thereof. Specific sizing agents foundparticularly suitable for use in the practice of this invention are:polyesters made by reaction of rosin-maleic anhydride adducts withaliphatic polyols such as ethylene glycol and glycerine, or with amixture of two or more such polyols. Suitable agents of this type arewell known, and many are commercially available. For example, theproduct sold commercially by Shanco Plastics & Chemicals, lnc., ofTonawanda, New York, under the brand name, SHANCO 4100 RESIN," has beenfound to be particularly satisfactory and is preferred for use. Thismaterial consists essentially of polyesters of the type herein disclosedas suitable for use as a sizing agent, and it has the following typicalproperties:

Molecular Weight 1000-2000 Melting Point (Ring and Ball Method) 147 C,-l57 C.

Acid Number l83-l93 Color Gardner (50 percent in Toluol) 5-7 SpecificGravity 0 25 C. 1.14

The surface application of the sizing agent can be effected convenientlyby conventional techniques and conventional equipment such as sizingequipment. Generally, the sizing agent is applied in the form of asolution, typically aqueous and alkaline. In the case of SHANCO 4 H30RESIN," for example, such solution consists of from about 4.0 to about16.0 percent by weight of the SHANCO 4100 RESlN" in a dilute aqueousalkali (pl-l 8-8.5), such as aqueous ammonium hydroxide, although aconcentration of approximately 8.0 percent has been found to beparticularly satisfactory and i: preferred. The aforedescribed aqueousalkaline solution of th( sizing agent is applied to the at leastpartially dried web 0 acid-contacted paper through the nip of aconventional size press applicator, and in an amount sufficient toresult in the addition on a water-free basis of from about 0.5 to about2.0 pounds of the sizing agent for each 3,000 square feet of paper(i.e., 500 sheets, each 24 inches X 36 inches). In the case of SHANCO4l00 RESIN," the addition of approximately [.0 pound of that sizingagent on a water-free basis per 3,000 square feet has been found to giveexcellent results.

Although a sizing agent such as "SHANCO 4100 RESIN" produces excellentresults when employed alone, it also may be used in combination withother suitable sizing agents.

Reference is again made to the accompanying figure for a schematicillustration of the sequence of operations in practicing the instantinvention in its several embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to illustrate aspecific and preferred embodiment of the invention, a paper base stockor furnish is prepared in a conventional manner comprising 100 weightpercent of a bleached hardwood pulp available commercially under thebrand name, ESPANOLA." This pulp is suitable for manufacturin g anabsorbent type of paper (commonly referred to as waterleaf"), whichtypically is used in the manufacture of parchment paper. In accordancewith the preferred practice of the invention, this furnish is modifiedso as to produce a superior base stock for making a more readilyerasable paper as herein disclosed. Specifically, there is incorporatedin such furnish approximately 5 percent of a titanium dioxide opacifyingfiller available commercially under the brand name, RAYOX,"approximately 0.25 percent ofa rosin size available commercially underthe brand name, CYFOR, approximately 0.25 percent of a melamineformaldehyde resin wet strength agent available commercially under thebrand name, PAREZ 607," and approximately 0.0625 percent of an opticalbrightening agent available commercially under the brand name, LEUCOFORB. The aforesaid percentages are by weight, and are based on dry pulp.After suitable preparation steps, such as beating, refining or both, themodified furnish so prepared is formed into an absorbent paper sheetmaterial by conventional machines and techniques of the Fourdriniertype.

The paper sheet material formed as above described is continuouslycontacted with a relatively concentrated aqueous solution of sulfuricacid, containing approximately 68 percent by weight of sulfuric acid,and is allowed to remain in contact therewith for a total contact timeof approximately 5 seconds. This contact is effected by continuouslyrunning the paper sheet material or web, submerged, through a liquidphase or bath consisting essentially of the above specified, relativelyconcentrated aqueous sulfuric acid solution, and, after emergence,allowing the paper to remain substantially wet with the acid solutionfor the balance of the specified S-second contact time. The temperatureof the bath, i.e., the contact temperature, is maintained relativelyconstant at about 60 F.

After emergence from the relatively concentrated aqueous sulfuric acidsolution, the paper is continuously contacted with a relatively andsubstantially more dilute aqueous solution of sulfuric acid, typicallycontaining approximately 35 percent or less by weight of sulfuric acid.As before, contacting conveniently can be effected by continuouslypassing the paper sheet material, submerged, through a liquid bathconsisting essentially of the relatively dilute aqueous sulfuric acid.However, this contacting preferably is effected countercurrently, bypassing the paper continuously through a countercurrent liquid streamwhich consists initially of water. In this case of contacting withdilute acid solution, the contacting need only be sufficiently long toaccomplish an adequate mixing of the two acid solutions. The contacttemperature is maintained in the range of from about 50 F. to about 100F.

After the paper sheet material emerges from the relatively diluteaqueous sulfuric acid solution, it is thoroughly washed, if necessarywith an excess of water, until substantially all of the acid is removed.Prior to a final water wash the paper web is contacted with an aqueousammonium hydroxide solution to remove remaining traces of acid andadjust the pH of the paper to approximately 8.0 to 8.5. The resultingpaper sheet material, substantially free of residual acid, then issubjected to drying by means of conventional equipment and techniques.

After at least partial drying, the surface application of a sizing agentis effected in the nip ofa conventional-size press applicator, throughwhich the at least partially dried web of acidtreated paper isprogressing. The sizing agent employed in this embodiment is thepolyester product available commercially fro m Shanco Plastics &Chemicals, lnc., under the brand name, SHANCO 4100 RESIN. The materialfor application consists essentially of a solution containingapproximately 8.0 percent by weight ofSHANCO 4100 RESIN in dilute aq uc'ous ammonium hydroxide (pH of 8.0 to 8.5). This solution of sizing agentis applied at the rate, on a dry basis, of approximately 1.0 pound ofthe solute resin per 3,000 square feet of paper. After application ofthe sizing agent, the web is further dried by means of conventionalequipment and techniques.

The paper prepared as above described then is subjected to comparativetesting: (a) with paper prepared identically and from the same paperstock, which paper has been acid contacted but has not been given asurface application of the sizing agent; and (b) with a conventional andstandard 25 percent rag pulp Bond paper available commercially andillustrative ofa typical high quality typewriter paper. To each of suchspecimens identical typewriting then is applied in a identical mannerand utilizing a single-use, carbon ribbon. Each specimen then isexamined or tested in substantially identical manner for: (l) uniformityor evenness of typewriting; (2) erasability; (3) resistance to inksmudging; and (4) resistance to ink feathering or wicking. The resultsof all such tests are evaluated and compared visually and in the samemanner. The following tabulation illustrates the results which areachieved:

As will be seen from the foregoing results, the product paper producedby practice of the acid-contacting technique of the invention exhibitsin both instances an erasability which is superior to that possessed bythe conventional Bond typewriter paper which is not so treated. However,it also will be noted that the paper stock which is subjected only tothe acid contacting step is inferior to the untreated conventional Bondpaper with respect to its resistance to ink smudging and feathering.Nevertheless, the paper stock which is subjected to the practice of thepresent invention in its preferred form, i.e., a combination of acidtreatment and surface sizing, exhibits excellent resistance to both inksmudging and feathering, and excellent receptivity to typewriting, inaddition to superior erasability. The observed superiority in evennessof type is particularly desirable, and unexpected, in view of thesomewhat poorer results in this regard achieved with other sizing agentstested. Results substantially similar in all respects are achieved whenthe same tests are conducted utilizing a cloth, multiuse, typewriterribbon instead ofa carbon ribbon.

It also should be noted that each of the papers described above, beingmade from a furnish which had been modified with additives in accordancewith the present invention, exhibits an opacity and whiteness renderingit of relatively superior quality for commercial sale and use as atypewriter paper.

When the above-described acid treatment and surface-sizing operationsare carried out in connection with papers produced without modificationof the furnish through the addition of additives, there is produced aproduct paper exhibiting substantially the same superior erasabilitycharacteristics and the same improved resistance to ink smudging andfeathering as the paper resulting from the practice of the instantinvention in its entirety. However, the paper produced without the stockmodification steps of the instant invention generally is not asdesirable commercially because of its relatively poorer opacity andwhiteness.

The invention claimed is:

1. Process for making an improved erasable paper which comprises:

a. forming a paper sheet from a cellulosic pulp;

b. contacting said paper sheet with an aqueous solution of sulfuric acidcontaining from about 60 to about 77 percent by weight of sulfuric acidfor a total contact time in the range of from about 1 to about 20seconds;

c. removing substantially all of said acid from the contacted paper; atleast partially drying said sheet; and

e. applying to the surface of said paper sheet a solution containing asizing amount in the range from about 4 percent to about 16 percent byweight, of a sizing composition consisting essentially of one or morepolyesters of rosins and maleic-anhydride adducts with polyhydricalcohols.

2. Process according to claim 1 wherein said sizing composition isapplied in an amount of from about 0.05 to about 2.0 pounds per 3,000square feet of dry paper sheet.

3. Process according to claim 1 wherein said sizing composition has anaverage molecular weight in the range of from about 1,000 to about2,000, a melting point in the range of from about 147 C. to about 157C., an acid number in the range of from about I 83 to about 193, and aspecific gravity at 25 C. of about H4, and is applied in an amount offrom about 0.05 to about 2.0 pounds per 3,000 square feet of dry papersheet.

4. Process according to claim 3, wherein said polyhydric alcohols arealiphatic polyols and including the steps of adding to said pulp abrightening amount of an optical brightcner and a filling amount of anopacifying tiller.

5. As an article of manufacture, improved erasable paper produced by aprocess which comprises:

a. forming a paper sheet from a cellulosic pulp;

b. contacting said paper sheet with an aqueous solution of sulfuric acidcontaining from about 60 to about 77 percent by weight of sulfuric acidfor a total contact time in the range of from about I to about 20seconds;

c. removing substantially all of said acid from the contacted P p atleast partially drying said sheet; and

e. applying to the surface of said paper sheet a solution con taining asizing amount in the range from about 4 percent to about 16 percent byweight, of a sizing composition consisting essentially of one or morepolyesters of rosins and maleic-anhydride adducts with polyhydricalcohols.

6. An article according to claim 5, wherein said paper sheet includes upto about 0. I25 percent by weight of the pulp on a dry basis of anoptical brightening agent and up to about 8 percent by weight of thepulp on a dry basis of an opacifying filler.

7. An article according to claim 5 wherein said polyester is applied inan amount of from about 0.05 to about 2.0 pounds per 3 ,000 square feetof dry paper sheet.

8. An article according to claim 5 wherein said polyester has an averagemolecular weight in the range of from about l,000 to about 2,000, amelting point in the range of from about 147 to about 157 C., an acidnumber in the range of from about 183 to about 193, and a specificgravity at 25 C. of about 1.14, and is applied in an amount of fromabout 0.05 to about 2.0 pounds per 3,000 square feet of dry paper sheet.

2. Process according to claim 1 wherein said sizing composition isapplied in an amount of from about 0.05 to about 2.0 pounds per 3,000square feet of dry paper sheet.
 3. Process according to claim 1 whereinsaid sizing composition has an average molecular weight in the range offrom about 1,000 to about 2,000, a melting point in the range of fromabout 147* C. to about 157* C., an acid number in the range of fromabout 183 to about 193, and a specific gravity at 25* C. of about 1.14,and is applied in an amount of from about 0.05 to about 2.0 pounds per3,000 square feet of dry paper sheet.
 4. Process according to claim 3,wherein said polyhydric alcohols are aliphatic polyols and including thesteps of adding to said pulp a brightening amount of an opticalbrightener and a filling amount of an opacifying filler.
 5. As anarticle of manufacture, improved erasable paper produced by a processwhich comprises: a. forming a paper sheet from a cellulosic pulp; b.contacting said paper sheet with an aqueous solution of sulfuric acidcontaining from about 60 to about 77 percent by weight of sulfuric acidfor a total contact time in the range of from about 1 to about 20seconds; c. removing substantially all of said acid from the contactedpaper; d. at least partially drying said sheet; and e. applying to thesurface of said paper sheet a solution containing a sizing amount in therange from about 4 percent to about 16 percent by weight, of a sizingcomposition consisting essentially of one or more polyesters of rosinsand maleic-anhydride adducts with polyhydric alcohols.
 6. An articleaccording to claim 5, wherein said paper sheet includes up to about0.125 percent by weight of the pulp on a dry basis of an opticalbrightening agent and up to about 8 percent by weight of the pulp on adry basis of an opacifying filler.
 7. An article according to claim 5wherein said polyester is applied in an amount of from about 0.05 toabout 2.0 pounds per 3,000 square feet of dry paper sheet.
 8. An articleaccording to claim 5 wherein said polyester has an average molecularweight in the range of from about 1,000 to about 2,000, a melting pointin the range of from about 147 to about 157* C., an acid number in therange of from about 183 to about 193, and a specific gravity at 25* C.of about 1.14, and is applied in an amount of from about 0.05 to about2.0 pounds per 3,000 square feet of dry paper sheet.